A bumper structure consisting of a beam extending transversely of a vehicle at the vehicle front, right and left mounting members attached to right and left ends of the beam, respectively, and right and left frame members mounted with the right and left mounting members, respectively, is disclosed in Japanese Patent Laid-Open Publication No. 2001-88633, for example. This bumper structure will be described below with reference to FIG. 7.
A bumper structure 100 includes an M-shaped cross-section beam 101 extending transversely of an automobile, and left and right polymeric corner members 104, 105 constituted by extruded members, fitted to left and right ends 102, 103 of the beam 101, respectively. The corner members 104, 105 are mounted to a vehicle frame (not shown) by a plurality of bolts 106.
This bumper structure 100, which is formed by rolling the beam 101 and then extruding the left and right corner members 104, 105 to the left and right ends of the beam 101, respectively, requires equipment in which a rolling mill (not shown) for the beam 101 is integrated with an extruding machine (not shown) for the left and right corner members 104, 105. The integration of the rolling mill and the extruding machine leads to large equipment, increasing the cost of equipment.
On the other hand, another method of attaching the left and right corner members 104, 105 to the beam 101 is possible as described below.
In this method, first, rolling of the beam 101 and extrusion of the left and right corner members 104, 105 are performed in separate steps. That is, the M-shaped beam 101 and the left and right corner members 104, 105 are manufactured separately.
Then, the left and right corner members 104, 105 manufactured by extrusion molding are inserted in a nested manner into the left and right ends 102, 103 of the beam 101 manufactured by rolling, to mount the left and right corner members 104, 105 to the left and right ends 102, 103 of the beam 101, respectively.
Thereafter, the corner members 104, 105 are mounted to the vehicle frame (not shown) by the bolts 106.
In this method, however, since the left and right corner members 104, 105 are inserted into the M-shaped beam 101, it is necessary to increase the precision of the beam 101 and the precision of the left and right corner members 104, 105. Accordingly, it is necessary to increase the machining accuracy of the rolling mill for rolling the beam 101 and the extruding machine for extruding the left and right corner members 104, 105, resulting in increased costs of the machines.
The left and right corner members 104, 105 attached to the left and right ends of the beam 101 are located at the left and right front corners of the automobile. On the right and left front corners of an automobile, an impact force will act obliquely from the front of the vehicle.
To deal with an oblique impact force from the front of the vehicle, it is preferable to form corners of the left and right corner members 104, 105 in a curved shape, and it is further preferable to increase the curvature of the curve.
However, like the beam 101, the left and right corner members 104, 105 are members extruded in a vehicle transverse direction. Therefore, it is difficult to form the corners (left and right ends) 102, 103 in a curved shape to deal with an oblique impact force from the front. In other words, it takes time to form the corners (left and right ends) 102, 103 of the left and right corner members 104, 105 in a curved shape, which prevents increase in productivity.
Further, the axial direction of extrusion in which the left and right corner members 104, 105 are extruded is the same direction as the extrusion direction of the beam 101. Therefore, even when the left and right corner members 104, 105 are inserted and fitted into opposite ends of the beam 101, the ends of the beam 101 and the laterally outer ends of the left and right corner members 104, 105 are in an open state. Consequently, an impact force applied obliquely from the front is not effectively transmitted to the vehicle frame.
Thus, there is a desire for a bumper beam structure which allows for reduced cost of equipment and increased productivity.